Display device

ABSTRACT

According to an aspect, a display device includes: a display panel including a display area provided with a plurality of pixels; and a light source configured to emit light to the display panel. Writing periods and lighting periods are alternately provided in one frame period for at least one color. Each writing period is a period in which part of a pixel signal is written to a corresponding one of the pixels. Each lighting period is a period in which light is emitted to the pixel after a corresponding one of the writing periods. A light amount in at least one of the lighting periods is larger than a light amount in other lighting periods.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority from Japanese PatentApplication No. 2019-208116 filed on Nov. 18, 2019 and InternationalPatent Application No. PCT/JP2020/042841 filed on Nov. 17, 2020, theentire contents of which are incorporated herein by reference.

BACKGROUND 1. Technical Field

What is disclosed herein relates to a display device.

2. Description of the Related Art

A display device using a polymer-dispersed liquid crystal has been known(for example, Japanese Patent Application Laid-open Publication No.2018-180196).

It has been requested to increase the number of gradations of an imagereproduced by a display device using a polymer-dispersed liquid crystal.

For the foregoing reasons, there is a need for a display device that ishigher in number of gradations.

SUMMARY

According to an aspect, a display device includes: a display panelincluding a display area provided with a plurality of pixels; and alight source configured to emit light to the display panel. Writingperiods and lighting periods are alternately provided in one frameperiod for at least one color. Each writing period is a period in whichpart of a pixel signal is written to a corresponding one of the pixels.Each lighting period is a period in which light is emitted to the pixelafter a corresponding one of the writing periods. A light amount in atleast one of the lighting periods is larger than a light amount in otherlighting periods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic circuit diagram illustrating a main configurationof a display device;

FIG. 2 is a schematic sectional view of a display panel;

FIG. 3 is a time chart illustrating exemplary field sequential controlin an embodiment;

FIG. 4 is a graph illustrating an exemplary gamma curve assumed for aneight-bit pixel signal;

FIG. 5 is a graph illustrating an exemplary relation between the numberof levels at each of which gradation control can be performed with thepixel signal and gradation expression in combination of the higher-orderbits (upper bits) and the lower-order bits (lower bits);

FIG. 6 is a time chart illustrating exemplary field sequential controlin a first modification;

FIG. 7 is a time chart illustrating exemplary field sequential controlin a second modification;

FIG. 8 is a time chart illustrating exemplary field sequential controlin a third modification;

FIG. 9 is a time chart illustrating exemplary field sequential controlin a fourth modification;

FIG. 10 is a time chart illustrating exemplary field sequential controlin a fifth modification; and

FIG. 11 is a time chart illustrating exemplary field sequential controlin a sixth modification.

DETAILED DESCRIPTION

An embodiment of the present disclosure will be described below withreference to the accompanying drawings. What is disclosed herein ismerely exemplary, and any modification that could be easily thought ofby the skilled person in the art as appropriate without departing fromthe gist of the disclosure is included in the scope of the presentdisclosure. In the drawings, the width, thickness, shape, and the likeof each component are schematically illustrated for clearer descriptionas compared to actual aspects in some cases, but are merely exemplaryand do not limit interpretation of the present disclosure. In thepresent specification and the drawings, any component same as thatalready described with reference to an already described drawing isdenoted by the same reference sign, and detailed description thereof isomitted as appropriate in some cases.

Embodiment

FIG. 1 is a schematic circuit diagram illustrating a main configurationof a display device 100. The display device 100 includes a display panelP and a light source device SL. The display panel P includes a displayarea 7, a signal output circuit 8, a scanning circuit 9, a VCOM drivecircuit 10, and a timing controller 13. Hereinafter, one surface of thedisplay panel P provided with the display area 7 is referred to as adisplay surface, and the other surface is referred to as a back surface.Sides of the display device 100 are positioned on both sides of thedisplay device 100 in a direction intersecting (for example, orthogonalto) a direction in which the display surface faces the back surface.

In the display area 7, a plurality of pixels Pix are disposed in amatrix (a row-column configuration). Each pixel Pix includes a switchingelement 1 and two electrodes. In FIG. 1 and FIG. 2 to be describedlater, a pixel electrode 2 and a common electrode 6 are illustrated asthe two electrodes.

FIG. 2 is a schematic sectional view of the display panel P. The displaypanel P includes two facing substrates and a liquid crystal 3 enclosedbetween the two substrates. Hereinafter, one of the two substrates isreferred to as a first substrate 30, and the other is referred to as asecond substrate 20.

The first substrate 30 includes a translucent glass substrate 35, thepixel electrodes 2 stacked on the second substrate 20 side of the glasssubstrate 35, and an insulating layer 55 stacked on the second substrate20 side to cover each of the pixel electrodes 2. The pixel electrode 2is provided individually for each pixel Pix. The second substrate 20includes a light-transmitting glass substrate 21, the common electrode 6stacked on the first substrate 30 side of the glass substrate 21, and aninsulating layer 56 stacked on the first substrate 30 side to cover thecommon electrode 6. The common electrode 6 has a plate or film shapewith which the common electrode 6 is shared by the pixels Pix.

The liquid crystal 3 of the embodiment is a polymer-dispersed liquidcrystal. Specifically, the liquid crystal 3 includes a bulk 51 and fineparticles 52. The orientations of the fine particles 52 change inaccordance with the potential difference between the pixel electrode 2and the common electrode 6 in the bulk 51. As the potential of the pixelelectrode 2 is controlled individually for each pixel Pix, at leasteither the degree of translucency or the degree of scattering iscontrolled for the pixel Pix.

In the embodiment described with reference to FIG. 2, the pixelelectrode 2 and the common electrode 6 face each other with the liquidcrystal 3 sandwiched therebetween, but the display panel P may have aconfiguration in which the pixel electrode 2 and the common electrode 6are provided to one substrate and the orientation of the liquid crystal3 is controlled by an electric field generated by the pixel electrode 2and the common electrode 6. The liquid crystal 3 may be a liquid crystalother than the polymer-dispersed liquid crystal.

The following describes a configuration for controlling the potentialsof the pixel electrode 2 and the common electrode 6. As illustrated inFIG. 1, the switching element 1 is a switching element using asemiconductor, such as a thin film transistor (TFT). One of the sourceand drain of the switching element 1 is coupled to one (the pixelelectrode 2) of the two electrodes. The other of the source and drain ofthe switching element 1 is coupled to a signal line 4. The gate of theswitching element 1 is coupled to a scanning line 5. Under control ofthe scanning circuit 9, the scanning line 5 provides potential foropening and closing the source-drain of the switching element 1. Thispotential control is performed by the scanning circuit 9.

In the example illustrated in FIG. 1, a plurality of the signal lines 4are arranged in one (row direction) of directions in which the pixelsPix are arranged. The signal lines 4 extend in the other arrangementdirection (column direction) of the pixels Pix. Each signal line 4 isshared by the switching elements 1 of more than one of the pixels Pixarranged in the column direction. A plurality of scanning lines 5 arearranged in the column direction. The scanning lines 5 extend in the rowdirection. Each scanning line 5 is shared by the switching elements 1 ofmore than one of the pixels Pix arranged in the row direction.

In description of the embodiment, the extending direction of thescanning lines 5 is referred to as an X direction, and the direction inwhich the scanning lines 5 are arranged is referred to as a Y direction.In FIG. 1, one of scanning lines 5 disposed at both ends in the Ydirection among the scanning lines 5 is referred to as a scanning line 5a, and the other is referred to as a scanning line 5 b.

The common electrode 6 is coupled to the VCOM drive circuit 10. The VCOMdrive circuit 10 provides a potential that functions as a commonpotential to the common electrode 6. When the signal output circuit 8outputs a signal to a signal line 4 at a timing at which the scanningcircuit 9 provides a potential that functions as a drive signal, to ascanning line 5, a storage capacitor formed between the correspondingpixel electrode 2 and the common electrode 6 and the liquid crystal(fine particles 52) as a capacitive load are charged. Thus, a voltagebetween the corresponding pixel Pix and the common electrode 6 becomes avoltage corresponding to a gradation signal to be described later. Afterthe drive signal becomes no longer provided, the storage capacitor andthe liquid crystal (fine particles 52) as the capacitive load holdstates corresponding to the signal output from the signal output circuit8. The scattering degree of the liquid crystal (fine particles 52) iscontrolled in accordance with the potential of each pixel Pix and thepotential of the common electrode 6. The liquid crystal 3 may be, forexample, a polymer-dispersed liquid crystal having a scattering degreethat increases as the difference between the potential of each pixel Pixand the potential of the common electrode 6 increases, or may be apolymer-dispersed liquid crystal having a scattering degree thatincreases as the difference between the potential of each pixel Pix andthe potential of the common electrode 6 decreases.

As illustrated in FIG. 2, the light source device SL is disposed on aside of the display panel P. The light source device SL includes a lightsource 11 and a light source drive circuit 12. The light source 11includes a first light source 11R configured to emit red light, a secondlight source 11G configured to emit green light, and a third lightsource 11B configured to emit blue light. The first light source 11R,the second light source 11G, and the third light source 11B each emitlight under control of the light source drive circuit 12. The firstlight source 11R, the second light source 11G, and the third lightsource 11B of the embodiment are each, for example, a light source usinga light emitting element such as a light emitting diode (LED), but thepresent disclosure is not limited thereto. Each light source may be anylight source, the light emission timing of which is controllable. Thelight source drive circuit 12 controls the light emission timings of thefirst light source 11R, the second light source 11G, and the third lightsource 11B under control of the timing controller 13.

When light is emitted from the light source 11, the display area 7 isilluminated with light incident from one side surface in the Ydirection. Each pixel Pix transmits or scatters the light incident fromone side surface in the Y direction. The degree of the scatteringdepends on the state of the liquid crystal 3 controlled in accordancewith a signal output from the signal output circuit 8.

The timing controller 13 is a circuit configured to control theoperation timings of the signal output circuit 8, the scanning circuit9, the VCOM drive circuit 10, and the light source drive circuit 12. Inthe embodiment, the timing controller 13 operates based on a signal thatis input through an input circuit 15.

The input circuit 15 outputs, to the timing controller 13 and the signaloutput circuit 8, a signal based on an input signal I (refer to FIG. 1)from the outside of the display device 100. When a signal indicating anRGB gradation value allocated to a pixel Pix is referred to as a pixelsignal, the input signal I that is input to the input circuit 15 inorder to output a frame image is a set of a plurality of pixel signalsfor the pixels Pix provided to the display area 7.

The input circuit 15 of the embodiment is, for example, a fieldprogrammable gate array (FPGA) mounted on a non-illustrated flexibleprinted board coupled to the display panel P or is a circuit that canimplement the same function. The input circuit 15 includes a memory 15 afor holding data of a frame image. The input circuit 15 outputs, fromthe frame image stored in the memory 15 a, a line image in a writingperiod of each field period in units of line images as described laterwith reference to FIG. 3 and other figures. In other words, the memory15 a needs to have a storage capacity capable of outputting line images,for example, in an order as described with reference to FIGS. 3 to 11.

A signal input from the input circuit 15 to the timing controller 13 maybe the input signal I or may be a signal indicating the input timing ofeither the input signal I from the input circuit 15 to the signal outputcircuit 8 or a signal generated based on the input signal I. It sufficesto obtain, from a signal input from the input circuit 15 to the timingcontroller 13, information necessary for controlling the output timingof a drive signal for providing the signal to each pixel Pix and theoperation timing of the signal output circuit 8.

The frame rate, in other words, the number of frame images displayed forone second (the number of times of frame image update) is any number andmay be, for example, 60 [Hz] in the embodiment.

FIG. 3 is a time chart illustrating exemplary field sequential controlin the embodiment. A frame period F1 of the embodiment includes aplurality of subframe periods. In the embodiment, the frame period F1includes a higher-order bit (upper bit) subframe period UB1 and alower-order bit (lower bit) subframe period LB2 as the subframe periods.The frame period F1 is a period in which operation of the display device100 for display of one frame image is performed. The higher-order bitsubframe period UB1 and the lower-order bit subframe period LB2 eachinclude field periods the number of which corresponds to the number ofcolors (for example, three) of the light source 11.

In FIG. 3, a first field period RF1, a second field period GF1, and athird field period BF1 are illustrated as the field periods of thehigher-order bit subframe period UB1. A first field period RF2, a secondfield period GF2, and a third field period BF2 are illustrated as thefield periods of the lower-order bit subframe period LB2. The firstfield period RF1, the second field period GF1, the third field periodBF1, the first field period RF2, the second field period GF2, and thethird field period BF2 each include the writing period W and a lightingperiod L.

The writing period W is a period in which part of a pixel signal iswritten to a pixel Pix. In the embodiment, the part of a pixel signal isa signal corresponding to the higher-order bits (i.e., upper bits) of agradation value indicated by a gradation signal or is a signalcorresponding to the lower-order bits (i.e., lower bits) of thegradation value. The gradation signal is a signal included in a pixelsignal and corresponding to the gradation value of any of red (R), green(G), and blue (B).

When q represents the number of bits of the gradation signal, the signalcorresponding to the higher-order bits is a signal in which the valuesof higher-order q/2 bits are the same as those of the gradation signaland the values of lower-order q/2 bits are all zero. The signalcorresponding to the lower-order bits is a signal in which the values ofhigher-order q/2 bits are all zero and the values of lower-order q/2bits are the same as those of the gradation signal. When the signalcorresponding to the higher-order bits and the signal corresponding tothe lower-order bits are added together, the original gradation signalin expression of a gradation value can be obtained. How to divide theoriginal gradation signal into the higher-order bits and the lower-orderbits is not limited to dividing the original gradation signal intohigher-order q/2 bits and lower-order q/2 bits. For example, thehigher-order bits may be the higher-order q/4 bits, and the lower-orderbits may be the remaining bits. The ratio between higher-order andlower-order bits is freely determined.

The lighting period L is a period in which light is emitted to the pixelafter the writing period W. Specifically, the pixel Pix is irradiatedwith light in a state in which the degree of light scattering by thepixel Pix is controlled in accordance with a signal written in thewriting period W. Thus, each pixel Pix of the display device 100 isilluminated with light in a color that is lit in the lighting period L,and scatters or blocks the light in a state corresponding to the signalwritten in the writing period W.

The lighting period L of each of the first field period RF1 and thefirst field period RF2 is a period in which red (R) light is emittedfrom the first light source 11R. The lighting period L of each of thesecond field period GF1 and the second field period GF2 is a period inwhich green (G) light is emitted from the second light source 11G. Thelighting period L of each of the third field period BF1 and the thirdfield period BF2 is a period in which blue (B) light is emitted from thethird light source 11B. In this manner, color reproduction can beperformed in combination of red (R), green (G), and blue (B) in thehigher-order bit subframe period UB1 and the lower-order bit subframeperiod LB2. In FIG. 3 and other drawings, a color of the light source 11that is turned on in a lighting period L is indicated by an alphabet inthe row of “light source (lighting)”.

The higher-order bit subframe period UB1 is a period in which the signalcorresponding to the higher-order bits of the gradation value indicatedby the gradation signal is written in each writing period W. Thelower-order bit subframe period LB2 is a period in which the signalcorresponding to the lower-order bits of the gradation value indicatedby the gradation signal is written in each writing period W.

The following describes an example of control related to a pixel Pixwhen an eight-bit gradation value of red (R), green (G), and blue (B),which is indicated by a pixel signal to be written to the pixel Pix in aframe period F1 is (R, G, B)=(255, 17, 1). In this description, thehigher-order bits are defined as the higher-order four bits in a bitvalue corresponding to the eight-bit gradation value indicating thegradation value of each color, and the lower-order bits are defined asthe lower-order four bits therein.

In the above-described example, the eight-bit gradation value (255) ofred (R) is “11111111” in expression of the values of eight bits. Thehigher-order bits are “11110000”, and the lower-order bits are“00001111”. Thus, in the writing period W included in the first fieldperiod RF1 of the higher-order bit subframe period UB1, a signal(potential) corresponding to “11110000” is provided to the pixel Pix. Inthe writing period W included in the first field period RF2 of thelower-order bit subframe period LB2, a signal (potential) correspondingto “00001111” is provided to the pixel Pix.

In the above-described example, the eight-bit gradation value (17) ofgreen (G) is “00010001” in expression of the values of eight bits. Thehigher-order bits are “00010000”, and the lower-order bits are“00000001”. Thus, in the writing period W included in the second fieldperiod GF1 of the higher-order bit subframe period UB1, a signal(potential) corresponding to “00010000” is provided to the pixel Pix. Inthe writing period W included in the second field period GF2 of thelower-order bit subframe period LB2, a signal (potential) correspondingto “00000001” is provided to the pixel Pix.

In the above-described example, the eight-bit gradation value (1) ofblue (G) is “00000001” in expression of the values of eight bits. Thehigher-order bits are “00000000”, and the lower-order bits are“00000001”. Thus, in the writing period W included in the third fieldperiod BF1 of the higher-order bit subframe period UB1, a signal(potential) corresponding to “00000000” is provided to the pixel Pix. Inthe writing period W included in the third field period BF2 of thelower-order bit subframe period LB2, a signal (potential) correspondingto “00000001” is provided to the pixel Pix.

While the degree of light scattering by the pixel Pix is controlled inaccordance with the signals (potentials) written to the pixel Pix inthis manner, light in colors corresponding to the written signals isemitted in the lighting periods L. The light amount in each lightingperiod L of the higher-order bit subframe period UB1 is larger than thelight amount in each lighting period L of the lower-order bit subframeperiod LB2. Specifically, when a gradation signal is divided into q/2higher-order bits and q/2 lower-order bits, the light amount in eachlighting period L of the higher-order bit subframe period UB1 is r timeslarger than the light amount in each lighting period L of thelower-order bit subframe period LB2. The number r is a value obtained byadding 1 to a maximum decimal value that can be expressed by thelower-order bits among the bits of the gradation signal. For example,when the number of bits of the gradation signal is eight, a maximumdecimal value that can be expressed by the lower-order bits is 15. Thus,the number r is 16. In this manner, the ratio between the light amountin each lighting period L of the higher-order bit subframe period UB1and the light amount in each lighting period L of the lower-order bitsubframe period LB2 corresponds to the number of bits of the gradationsignal. When the number of bits of the gradation signal is q, thehigher-order bits are higher-order t bits among the q bits, and thelower-order bits are the remaining bits, the light amount ratio can beexpressed as 2 t:1. For example, when the number q is eight, thehigher-order bits are four bits, and the lower-order bits are four bits,the ratio between the light amount in the higher-order bit lightingperiod and the light amount in the lower-order bit lighting period is16:1. When the number q is eight, the higher-order bit is one bit, andthe lower-order bits are seven bits, the ratio between the light amountin the higher-order bit lighting period and the light amount in thelower-order bit lighting period is 2:1.

The light amount is determined by the luminance, which is the strengthof light per unit time, and the time of light irradiation. When theluminance of the light source 11 is constant, the light amount is equalto the luminance×a lighting period. In this case, the light amount issmaller as the lighting period, in other words, the time of lightirradiation, is shorter; and the light amount is larger as the lightingperiod is longer. In the embodiment, the light amount is controlled by,for example, the length of the lighting period of the light source 11.FIG. 3 schematically illustrates that the time length of each lightingperiod L included in the higher-order bit subframe period UB1 is longerthan the time length of each lighting period L included in thelower-order bit subframe period LB2. Although FIG. 3 is not illustratedwith the ratio (16:1) between the higher-order bits and the lower-orderbits, which precisely corresponds to the above-described example; inreality, the time length of each lighting period L included in thehigher-order bit subframe period UB1 and the time length of eachlighting period L included in the lower-order bit subframe period LB2are set so as to correspond to the ratio between the higher-order bitsand lower-order bits.

As described above, in the embodiment, in the first field period RF1,the pixel Pix is controlled in the writing period W in accordance withthe higher-order bits of red (R) of the gradation signal, and red (R)light of the light amount corresponding to the higher-order bits isemitted from the first light source 11R in the lighting period L. In thesecond field period GF1, the pixel Pix is controlled in the writingperiod W in accordance with the higher-order bits of green (G) of thegradation signal, and green (G) light of the light amount correspondingto the higher-order bits is emitted from the second light source 11G inthe lighting period L. In the third field period BF1, the pixel Pix iscontrolled in the writing period W in accordance with the higher-orderbits of blue (B) of the gradation signal, and blue (B) light of thelight amount corresponding to the higher-order bits is emitted from thethird light source 11B in the lighting period L. Thus, colorreproduction is performed in combination of red (R), green (G), and blue(B) corresponding to the higher-order bits of the gradation signal inthe entire higher-order bit subframe period UB1.

In the first field period RF2, the pixel Pix is controlled in thewriting period W in accordance with the lower-order bits of red (R) ofthe gradation signal, and red (R) light of the light amountcorresponding to the lower-order bits is emitted from the first lightsource 11R in the lighting period L. In the second field period GF2, thepixel Pix is controlled in the writing period W in accordance with thelower-order bits of green (G) of the gradation signal, and green (G)light of the light amount corresponding to the lower-order bits isemitted from the second light source 11G in the lighting period L. Inthe third field period BF2, the pixel Pix is controlled in the writingperiod W in accordance with the lower-order bits of blue (B) of thegradation signal, and blue (B) light of the light amount correspondingto the lower-order bits is emitted from the third light source 11B inthe lighting period L. Thus, color reproduction is performed incombination of red (R), green (G), and blue (B) corresponding to thelower-order bits of the gradation signal in the entire lower-order bitsubframe period LB2. Consequently, color reproduction is performed incombination of red (R), green (G), and blue (B) corresponding to thegradation signal in the entire frame period F1 including thehigher-order bit subframe period UB1 and the lower-order bit subframeperiod LB2.

The pixel Pix control in each writing period W is performed for each ofthe pixels Pix in accordance with the gradation signal providedindividually to the pixel Pix.

Specifically, signal writing in each writing period W is performed inunits of a plurality of pixels Pix (pixel row) arranged in the Xdirection and sharing a scanning line 5 as illustrated in FIG. 1. Morespecifically, at a timing when the drive signal is provided to ascanning line 5, pixels Pix coupled to the scanning line 5 are driven,and at this timing, an individual signal is provided to each of thesignal lines 4 arranged in the X direction. Thus, the individual signalsare written to the pixels Pix included in a pixel row and sharing thescanning line 5.

In FIG. 3, signals written on a pixel row basis as described above areillustrated with rectangles in the time chart. For example, “Rhigher-order line 1” represents signals (line 1) for one pixel row,which are written to pixels Pix included in a pixel row coupled to thescanning line 5 (for example, the scanning line 5 a) positioned at oneend of the display area 7 in the Y direction in the writing period W ofthe first field period RF1. In addition, “R higher-order line 2”represents signals (line 2) for one pixel row, which are written topixels Pix included in a pixel row coupled to the second scanning line 5counting from the one end of the display area 7 in the Y direction inthe writing period W of the first field period RF1. In addition, “Rhigher-order line N−1” represents signals (line N−1) for one pixel row,which are written to pixels Pix included in a pixel row coupled to thesecond-to-last scanning line 5 counting from the one end of the displayarea 7 in the Y direction in the writing period W of the first fieldperiod RF1. In addition, “R higher-order line N” represents signals(line N) for one pixel row, which are written to pixels Pix included ina pixel row coupled to the last scanning line 5 (for example, thescanning line 5 b) counting from the one end of the display area 7 inthe Y direction, that is, the scanning line 5 positioned at the otherend, in the writing period W of the first field period RF1.

The letter “R” included in illustrations of rectangles such as “Rhigher-order line 1”, “R higher-order line 2”, . . . , “R higher-orderline N−1”, and “R higher-order line N” described above indicates thatthe gradation signal is a signal corresponding to the red (R) colorincluded in the pixel signal. For example, the letter “G” included inillustrations of rectangles such as “G higher-order line 1”, “Ghigher-order line 2”, . . . , “G higher-order line N−1”, and “Ghigher-order line N” in the second field period GF1 indicates that thegradation signal is a signal corresponding to the green (G) colorincluded in the pixel signal. The letter “B” included in illustrationsof rectangles such as “B higher-order line 1”, “B higher-order line 2”,. . . , “B higher-order line N−1”, and “B higher-order line N” in thethird field period BF1 indicates that the gradation signal is a signalcorresponding to the blue (B) color included in the pixel signal.

The word “higher-order” included in illustrations of rectangles such as“R higher-order line 1”, “R higher-order line 2”, . . . , “Rhigher-order line N−1”, “R higher-order line N”, “G higher-order line1”, “G higher-order line 2”, . . . , “G higher-order line N−1”, “Ghigher-order line N”, “B higher-order line 1”, “B higher-order line 2”,. . . , “B higher-order line N−1”, and “B higher-order line N” describedabove indicates a signal corresponding to the higher-order bits. Forexample, the word “lower-order” included in illustrations of rectanglessuch as “R lower-order line 1”, “R lower-order line 2”, . . . , “Rlower-order line N−1”, “R lower-order line N”, “G lower-order line 1”,“G lower-order line 2”, . . . , “G lower-order line N−1”, “G lower-orderline N”, “B lower-order line 1”, “B lower-order line 2”, . . . , “Blower-order line N−1”, and “B lower-order line N” in the lower-order bitsubframe period LB2 indicates a signal corresponding to the lower-orderbits.

Arrows SL1 and SL2 in FIG. 3 and other drawings each represent scanningperformed in the first writing period W of the corresponding frameperiod F1. Scanning means operation that sequentially shifts a drivesignal output target from either the scanning line 5 a or the scanningline 5 b to the other one. Such arrows pointing from one end side of thedisplay area to the other end side, including other arrows denoted by noreference sign, represent scanning performed in the correspondingwriting periods W. Although not illustrated, when an image is updated inaccordance with a frame rate, a plurality of frame periods F1corresponding to the frame rate are provided so as to be continuous intime.

Through the above-described pixel Pix control divided into thehigher-order bits control and the lower-order bits control, it ispossible to handle a pixel signal that is input as a signal havinggradation levels the number of which is larger than the number of levelsat each of which gradation control can be performed in one writingperiod W for a pixel Pix.

FIG. 4 is a graph illustrating an exemplary gamma curve assumed for aneight-bit pixel signal. FIG. 5 is a graph illustrating an exemplaryrelation between the number of levels at each of which the gradationcontrol can be performed with a pixel Pix and gradation expression incombination of the higher-order bits and the lower-order bits.

In the gradation control by light scattering degree control using apolymer-dispersed liquid crystal as in the embodiment, voltagecorresponding to the number of gradations (256; 0 to 255) with aneight-bit pixel signal as illustrated in FIG. 4 needs to be directlyprovided to the polymer-dispersed liquid crystal. In this case, acircuit that drives the polymer-dispersed liquid crystal needs to outputvoltages of 256 gradations, which complicates the circuit. However, whenthe eight-bit pixel signal is divided into two, namely, a signalcorresponding to the higher-order bits and a signal corresponding to thelower-order bits, each signal can be handled as a four-bit signal ineffect. The number of gradations necessary for gradation expression withfour bits is 16 (0 to 15), and the circuit that drives thepolymer-dispersed liquid crystal only needs to output 16 gradations. Inthe embodiment, based on such an idea, the higher-order bit subframeperiod UB1 for performing the gradation control based on the signalcorresponding to the higher-order bits and the lower-order bit subframeperiod LB2 for performing the gradation control based on the signalcorresponding to the lower-order bits are provided in the frame periodF1.

First, in the higher-order bit subframe period UB1, control is performedbased on the signal corresponding to the higher-order bits so that thedegree of light scattering (or blocking) of each pixel Pix correspondsto any of the 16 levels. Subsequently, in the lower-order bit subframeperiod LB2, control is performed based on the signal corresponding tothe lower-order bits so that the degree of light scattering (orblocking) of each pixel Pix corresponds to any of the 16 levels. Asdescribed above, the light amount in the lighting period L of thehigher-order bit subframe period UB1 is r times larger than the lightamount in the lighting period L of the lower-order bit subframe periodLB2. The number r is 16 when the total number of bits is eight, thehigher-order bits are four bits, and the lower-order bits are four bits.

When the 16 levels of the gradation control based on the light amountfor the lower-order bits are expressed with the 16 values of “0, 1, 2,3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15”, the values of the 16levels of the gradation control with the higher-order bits that provider times (r=16) the amount of light provided by the lower-order bits, are“0, 16, 32, 48, 64, 80, 96, 112, 128, 144, 160, 176, 192, 208, 224, and240”. Thus, 256 levels of 0 to 255 can be expressed with a combined useof the higher-order bits and the lower-order bits. For example, the 16levels of “0 to 15” can be expressed by changing the lower-order bits to“0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15” while thehigher-order bits is set to “0” and deriving the values of thehigher-order bits+the lower-order bits. Specifically, it is possible toperform the gradation control corresponding to the gradation value of“1” with a pixel Pix by performing the gradation control correspondingto “0” in the higher-order bit subframe period UB1 and performing thegradation control corresponding to “1” in the lower-order bit subframeperiod LB2. In addition, it is possible to perform the gradation controlcorresponding to the gradation value of “7” with a pixel Pix byperforming the gradation control corresponding to “0” in thehigher-order bit subframe period UB1 and performing the gradationcontrol corresponding to “7” in the lower-order bit subframe period LB2.In the same manner, the lower-order bits are changed while thehigher-order bits are set to any of “0, 16, 32, 48, 64, 80, 96, 112,128, 144, 160, 176, 192, 208, 224, and 240”. Thus, the 256 levels of 0to 255 can be expressed with a combined use of the higher-order bits andthe lower-order bits, for example, “16 to 31” with the higher-order bitsset to “1”, “32 to 47” with the higher-order bits set to “2”, . . . .

In FIG. 5, gradation ranges when the value of the higher-order bits is0, 16, 32, . . . , 240, are denoted as ranges U01, U02, U03, . . . ,U16, respectively. A black band in each range represents the gradationcontrol of the pixel Pix corresponding to the value of the higher-orderbits. The ratio between the amount of light emitted in the lightingperiod L in a state of the gradation control of the pixel Pixcorresponding to the above-mentioned value of the higher-order bits andthe amount of light emitted in the lighting period L in a state of thegradation control of the pixel Pix corresponding to the value (0, 1, 2,. . . , 16) of the lower-order bits is 16:1. Thus, the degree of lightthat is scattered (or blocked) in the frame period F1 is controlled soas to correspond to the number of bits (eight bits) of the pixel signal.Although FIG. 5 illustrates the four lower-order bits with a 16 stepgradation with dotted lines, the light amount in the lighting periodcorresponding to the lower-order bits is 1/16 times as large as thelight amount in the lighting period corresponding to the higher-orderbits as described above. Thus, each gradation visually recognized in theframe period F1 corresponds to the sum of the light amount that is setto 1/16 times as large as the light amount for the higher-order bitsthrough the lighting period corresponding to the lower-order bits andthe light amount corresponding to a gradation of the higher-order bitsillustrated with a solid line.

The above description is made with the example in which the number oflevels of the gradation control of the pixel Pix is 16 and the pixelsignal is an eight-bit signal, but the present disclosure is not limitedthereto. The present disclosure is also applicable to a combination ofanother number of bits of the pixel signal and another number of levelsof the gradation control of the pixel Pix, when y, which represents thenumber of bits of the pixel signal, is replaced with the square root ofx and x is applied as the number of levels of the gradation control ofthe pixel Pix.

As described above, according to the embodiment, the display device 100includes the display panel P including the display area provided with aplurality of pixels Pix, and the light source 11 configured to emitlight to the display panel P. The writing periods W and the lightingperiods L are alternately provided in one frame period F1 for at leastone color. Each writing period W is a period in which part of a pixelsignal is written to a corresponding one of the pixels Pix. Eachlighting period L is a period in which light is emitted to the pixelsPix after a corresponding one of the writing periods W. The light amountin at least one of the lighting periods L is larger than the lightamount in other lighting periods. A larger number of gradations can beexpressed with such a combination of at least one lighting period L, inwhich the light amount is larger than in other lighting periods L, andother lighting periods L. Thus, the display device 100 that is higher innumber of gradations can be provided.

The light source 11 includes the first light source 11R, the secondlight source 11G, and the third light source 11B. The writing periods Wand the lighting periods L are provided for each of red (R), green (G),and blue (B). Since such combination of one lighting period L, in whichthe light amount is larger than in other lighting periods L, and otherlighting periods L is provided for each color, a color image can bedisplayed with a larger number of gradations.

The light amount in one lighting period L, in which the light amount islarger than in other lighting periods L, corresponds to the higher-orderbits of the pixel signal, and the light amount in other lighting periodsL corresponds to the lower-order bits of the pixel signal. Thus, alarger number of gradations can be expressed by simple signal controlbased on the pixel signal.

When the display device is configured such that the light amount dependson the lighting time of the light source 11, light amount control can beperformed by time length control of each lighting period L, which issimple control.

When the display device is configured such that the light amount dependson the luminance of the light source 11, light amount control can beperformed more flexibly in time, without restrictions on the time lengthof each lighting period L. Light amount control may be performed with acombined use of the lighting time control of the light source 11 and theluminance control thereof. As described above, the light amount isdetermined by the luminance and the lighting period. When the luminanceor lighting period of the light source 11 is constant, the light amountis equal to the luminance x the lighting period. Thus, the light amountmay be controlled based on the lighting period while the luminance iskept constant, the light amount may be controlled based on the luminancewhile the lighting period is kept constant, or the light amount may becontrolled with both the luminance and the lighting period as variables.

In the display panel P, the polymer-dispersed liquid crystal (liquidcrystal 3) is enclosed between two facing substrates (the secondsubstrate 20 and the first substrate 30). Thus, the display device 100that is higher in number of gradations can be provided with aconfiguration using a polymer-dispersed liquid crystal, which tends tohave technological difficulties in multi-gradation control.

MODIFICATIONS

The following sequentially describes modifications of the embodimentwith reference to FIGS. 6 to 11.

First Modification

FIG. 6 is a time chart illustrating exemplary field sequential controlin a first modification. The first modification is the same as theembodiment except that the lower-order bit subframe period LB2 in theembodiment is replaced with a lower-order bit subframe period LB3. Thelower-order bit subframe period LB3 is the same as the lower-order bitsubframe period LB2 except for features noted below. For example, thelower-order bit subframe period LB3 includes field periods the number ofwhich corresponds to the number of colors (for example, three) of thelight source 11. In FIG. 6, a first field period RF3, a second fieldperiod GF3, and a third field period BF3 are illustrated as the fieldperiods of the lower-order bit subframe period LB3.

In each writing period W of the lower-order bit subframe period LB3,signal writing in the writing period W is performed in units of at leasttwo pixel rows. More specifically, at a timing when drive signals areprovided to at least two scanning lines 5 adjacent to each other in theY direction, pixels Pix coupled to the scanning lines 5 are driven, andat this timing, an individual signal is provided to each of the signallines 4 arranged in the X direction. Thus, the individual signals arewritten to a plurality of pixels Pix included in pixel rows coupled tothe at least two scanning lines 5. The same signal is provided to thetwo pixels Pix sharing one signal line 4. In other words, the samesignal is provided to at least two pixels Pix adjacent to each other inthe Y direction.

In FIG. 6, signals written in units of two pixel rows are illustratedwith rectangles in the time chart. For example, “lower-order line 1”represents signals written to pixels Pix included in pixel rows coupledto at least two scanning lines 5 including the scanning line 5 (forexample, the scanning line 5 a) positioned at the one end of the displayarea 7 in the Y direction and another scanning line 5 adjacent to thescanning line 5 in the writing period W of the first field period RF3.In addition, “lower-order line N” represents signals written to pixelsPix included in pixel rows coupled to at least two scanning lines 5including the last scanning line 5 (for example, the scanning line 5 b)counting from the one end of the display area 7 in the Y direction, thatis, the scanning line 5 positioned at the other end, and anotherscanning line 5 adjacent to the last scanning line 5 in the writingperiod W of the first field period RF3.

Alternatively, “lower-order line 1” may represent signals written topixels Pix included in a pixel row coupled to the scanning line 5 (forexample, the scanning line 5 a) positioned at the one end of the displayarea 7 in the Y direction in the lower-order bit subframe period LB2 inthe embodiment. Alternatively, “lower-order line 1” may representsignals written to pixels Pix included in a pixel row coupled to anotherscanning line 5 adjacent to the scanning line 5 positioned at the oneend in the lower-order bit subframe period LB2 in the embodiment.Alternatively, “lower-order line 1” may represent the average of theformer lower-order bit value and the latter lower-order bit valuedescribed above as examples of “lower-order line 1”. Specifically, thelower-order bits of pixel signals for a predetermined number (n) ofpixels Pix arranged in a first direction (the Y direction) may beaveraged, and the average signal is written at a time to each of thepredetermined number of pixels Pix arranged in the first direction. Itshould be noted that n is a natural number equal to or larger than 2.For example, the number n is 2 but may be equal to or larger than 3.

Similarly, “lower-order line N” may represent signals written to pixelsPix included in a pixel row coupled to the scanning line 5 (for example,the scanning line 5 b) positioned at the other end of the display area 7in the Y direction in the lower-order bit subframe period LB2 in theembodiment. Alternatively, “lower-order line N” may represent signalswritten to pixels Pix included in a pixel row coupled to anotherscanning line 5 adjacent to the scanning line 5 positioned at the otherend in the lower-order bit subframe period LB2 in the embodiment.Alternatively, “lower-order line N” may be the average of the formerlower-order bit value and the latter lower-order bit value. Although notillustrated, the same configuration described above applies to signalcontrol in signal writing in units of two pixel rows between the one endand the other end.

As for “lower-order line 1” and “lower-order line N” in the writingperiod W of the second field period GF3, and as for “lower-order line 1”and “lower-order line N” in the writing period W of the third fieldperiod BF3, the configurations thereof are the same as that in thewriting period W of the first field period RF3 except for the colorscorresponding to the signals.

In FIG. 6 and FIGS. 7, 8, and 9 to be described later, illustrations ofsymbols (R, G, and B) indicating colors are omitted from rectanglesrepresenting signals for one pixel row, which are written to pixels Pixin field periods other than the higher-order bit subframe period UB1.However, in reality, in the writing period W of each field period,signals corresponding to the color (R, G, or B) of light to be emittedimmediately after the writing period W are written.

According to the first modification, in the display area 7, a pluralityof pixel rows are arranged in the first direction (Y direction). Eachpixel row includes a plurality of pixels Pix arranged in a seconddirection (X direction) orthogonal to the first direction. Thelower-order bits of pixel signals are written at a time to apredetermined number of pixels Pix arranged in the first direction. Thepredetermined number is equal to or larger than two. This reduces thescanning time of each writing period W for writing signals correspondingto the lower-order bits and can increase time allocated to any otherprocess performed in the frame period F1. Consequently, it becomeseasier to increase the length of each lighting period L and ensure theluminance of display output. The scanning time is time from start tocompletion of scanning.

When the lower-order bits of pixel signals for a predetermined number(n) of pixels Pix arranged in the first direction (Y direction) areaveraged and written at a time to the predetermined number of pixels Pixarranged in the first direction, information of the input signal I forthe predetermined number of pixels Pix to which signals aresimultaneously written can be averaged and reflected. Thus, it ispossible to restrain information from being discarded between inputtingand outputting.

Second Modification

FIG. 7 is a time chart illustrating exemplary field sequential controlin a second modification. The second modification is the same as theembodiment except that the lower-order bit subframe period LB2 in theembodiment is replaced with a lower-order bit subframe period LB4 and alower-order bit subframe period LB5. Specifically, the frame period F1of the second modification includes the higher-order bit subframe periodUB1, the lower-order bit subframe period LB4, and the lower-order bitsubframe period LB5.

In each writing period W of the lower-order bit subframe period LB4 andeach writing period W of the lower-order bit subframe period LB5, signalwriting in the writing period W is performed in units of two pixel rowsin the same manner as the writing period W of the lower-order bitsubframe period LB3. In the second modification, signals written in eachwriting period W of the lower-order bit subframe period LB4 and signalswritten in each writing period W of the lower-order bit subframe periodLB5 are set so that control of each pixel Pix in accordance with asignal corresponding to eight lower-order bits is performed withcombination of the writing period W of the lower-order bit subframeperiod LB4 and the writing period W of the lower-order bit subframeperiod LB5.

For example, “lower-order 1 line 1” in FIG. 7 represents signals writtento pixels Pix included in pixel rows coupled to at least two scanninglines 5 including the scanning line 5 (for example, the scanning line 5a) positioned at the one end of the display area 7 in the Y directionand another scanning line 5 adjacent to the scanning line 5 in thewriting period W of a first field period RF4. In addition, “lower-order2 line 1” in FIG. 7 represents signals written to pixels Pix included inpixel rows coupled to at least two scanning lines 5 including thescanning line 5 (for example, the scanning line 5 a) positioned at theone end of the display area 7 in the Y direction and another scanningline 5 adjacent to the scanning line 5 in the writing period W of afirst field period RF5. The idea of signal control in units of at leasttwo pixel rows in the second modification is the same as in the firstmodification.

In the second modification, a signal corresponding to the lower-orderbits is divided into “lower-order 1 line 1” and “lower-order 2 line 1”.The signal corresponding to the lower-order bits may be divided in anygiven manner. For example, the “least significant bit of the signalcorresponding to the lower-order bits” may be allocated to “lower-order2 line 1” and “bits except for the least significant bit of the signalcorresponding to the lower-order bits” may be allocated to “lower-order1 line 1”, or the same number of bits may be allocated to each line. Forexample, when the gradation signal is an eight-bit signal and the signalcorresponding to the lower-order bits is “00000101”, the “leastsignificant bit of the signal corresponding to the lower-order bits” is“00000001” and the “bits except for the least significant bit of thesignal corresponding to the lower-order bits” are “00000100”.

The ratio between the light amount in each lighting period L of thelower-order bit subframe period LB4 and the light amount in eachlighting period L of the lower-order bit subframe period LB5 correspondsto the manner of division of a signal corresponding to the lower-orderbits. When the signal is divided into the “least significant bit of thesignal corresponding to the lower-order bits” and the “bits except forthe least significant bit of the signal corresponding to the lower-orderbits” as described above and the number of lower-order bits is four, theratio between the light amount in each lighting period L of thelower-order bit subframe period LB4 and the light amount in eachlighting period L of the lower-order bit subframe period LB5 is 8:1.However, the ratio is not limited thereto and may be changed asappropriate.

In FIG. 7, “lower-order 1 line N” represents signals written to pixelsPix included in pixel rows coupled to at least two scanning lines 5including the last scanning line 5 (for example, the scanning line 5 b)counting from the one end of the display area 7 in the Y direction, thatis, the scanning line 5 positioned at the other end, and anotherscanning line 5 adjacent to the last scanning line 5 in the writingperiod W of the first field period RF4. In addition, “lower-order 2 lineN” represents signals written to pixels Pix included in pixel rowscoupled to at least two scanning lines 5 including the last scanningline 5 (for example, the scanning line 5 b) counting from the one end ofthe display area 7 in the Y direction, that is, the scanning line 5positioned at the other end, and another scanning line 5 adjacent to thelast scanning line 5 in the writing period W of the first field periodRF5. The relation between “lower-order 1 line N” and “lower-order 2 lineN” is the same as the relation between “lower-order 1 line 1” and“lower-order 2 line 1”.

As illustrated in FIG. 7, when a subframe period in which signalscorresponding to the lower-order bits are written is divided into aplurality of periods, the number of gradations can be further increased.The increase in number of subframe periods leads to increase in numberof writing periods W provided in the frame period F1, and consequently,the ratio of the scanning time in each writing period W relative to theframe period F1 increases. To address this, signal writing issimultaneously performed for a predetermined number (n) of pixel rows asin the lower-order bit subframe period LB4 and the lower-order bitsubframe period LB5, whereby the scanning time is shortened to about 1/nof that for signal writing performed on a pixel row basis.

According to the second modification, two writing periods W and twolighting periods L corresponding to the lower-order bits of the pixelsignal are provided in one frame period F1. Thus, it is possible toperform gradation expression closer to a gamma curve while restrainingincrease in the scanning time along with increase in number of thesubframe periods.

In the description with reference to FIG. 7, the lower-order bitsubframe period LB4 and the lower-order bit subframe period LB5 areprovided as an example when the number (n) of subframe periods for asignal corresponding to the lower-order bits is two, but the number nmay be equal to or larger than three. In this case, a subframe period isprovided in which, for example, “lower-order 1 line 1”, “lower-order 2line 1”, . . . , “lower-order n line 1” are written in units of n pixelrows in each writing period W.

Third Modification

FIG. 8 is a time chart illustrating exemplary field sequential controlin a third modification. The third modification is the same as theembodiment except that a lower-order bit subframe period LB6 is providedas an additional subframe period after the lower-order bit subframeperiod LB3 in the first modification.

Specifically, the frame period F1 of the third modification includes thehigher-order bit subframe period UB1, the lower-order bit subframeperiod LB3, and the lower-order bit subframe period LB6.

The lower-order bit subframe period LB6 is used for extended gradationexpression that is not included in the original gradation signal asgradation value expression. For example, the gradation signal is aneight-bit signal, the least significant bit (1 or 0) is additionallyprovided for the writing period W of the lower-order bit subframe periodLB6, and thus gradation performance of image display can be furtherimproved. In the third modification, the ratio between the light amountin each lighting period L of the higher-order bit subframe period UB1,the light amount in each lighting period L of the lower-order bitsubframe period LB3, and the light amount in each lighting period L ofthe lower-order bit subframe period LB6 is, for example, 2^((y+1)):2:1.However, the ratio is not limited thereto but may be changed asappropriate.

The lower-order bit subframe period LB6 can be used for, for example, aconfiguration with which the number of gradations can be furtherincreased like a high dynamic range (HDR), correction of variance incharacteristics (the degree of light scattering) among the pixels Pix inthe display area 7, and adjustment of luminance gradient. The luminancegradient is luminance non-uniformity in luminance distribution betweenthe light source 11 side and the opposite side caused by occurrence of atendency that the degree of light scattering is higher on the lightsource 11 side (at a position closer to the light source 11) and islower on the opposite side (at a position farther from the light source11) like an LED (a tendency that light becomes weaker from the lightsource 11 side toward the opposite side is expressed as gradient). Basedon the luminance gradient, the scattering degree of the liquid crystalcloser to the opposite side farther from the light source 11 isincreased by controlling voltage to be applied to the pixels Pix closerto the opposite side, whereby the scattering degree can be made entirelyuniform. With such control, the luminance gradient can be adjusted. Inthe embodiment, the actual (analog) luminance gradient in which theluminance is continuously changed is adjusted by controlling the(digital) gradation value that is changed in a step-wise manner. Thus,by further increasing the number of the gradations, it is possible tocontrol the gradation value of the pixel more finely, which can make thegradation of the luminance gradient adjustment indistinctive.

In FIG. 8, “additional L1” represents signals written to pixels Pixincluded in pixel rows coupled to at least two scanning lines 5including the scanning line 5 (for example, the scanning line 5 a)positioned at the one end of the display area 7 in the Y direction andanother scanning line 5 adjacent to the scanning line 5 in the writingperiod W of a first field period RF6. The idea of signal control inunits of at least two pixel rows in the lower-order bit subframe periodLB6 in the third modification is the same as that for the lower-orderbit subframe period LB3 of the first modification.

Fourth Modification

FIG. 9 is a time chart illustrating exemplary field sequential controlin a fourth modification. The fourth modification is the same as theembodiment except that a lower-order bit subframe period LB7 is providedas an additional subframe period after the lower-order bit subframeperiod LB3 in the first modification. Specifically, the frame period F1of the fourth modification includes the higher-order bit subframe periodUB1, the lower-order bit subframe period LB3, and the lower-order bitsubframe period LB7.

The lower-order bit subframe period LB7 is provided for writingunwritten signals when signals that would be written in a case of thelower-order bit subframe period LB2 are not written to the lower-orderbit subframe period LB3 because signal control is performed in units ofn pixel rows in the lower-order bit subframe period LB3. For example,when “lower-order line 1” in the lower-order bit subframe period LB3represents signals written to pixels Pix included in a pixel row coupledto the scanning line 5 (for example, the scanning line 5 a) positionedat the one end of the display area 7 in the Y direction in thelower-order bit subframe period LB2 (refer to FIG. 3) of the embodiment,“lower-order 2 line 2” in the lower-order bit subframe period LB7represents signals written to pixels Pix included in a pixel row coupledto another scanning line 5 adjacent to the scanning line 5 positioned atthe one end in the lower-order bit subframe period LB2 (refer to FIG. 3)of the embodiment.

In the lower-order bit subframe period LB7, pixel rows to which signalsare written in units of n pixel rows are shifted by one row from thosein the lower-order bit subframe period LB3. For example, “lower-order 2line 2” in FIG. 9 represents signals written to pixels Pix included inpixel rows coupled to two scanning lines 5 including a “second scanningline 5” adjacent to the scanning line 5 (for example, the scanning line5 a) positioned at the one end of the display area 7 in the Y direction,and a scanning line 5 (third scanning line 5) adjacent to the “secondscanning line 5” but not positioned at the one end in the writing periodW of a first field period RF7. In addition, “lower-order 2 LN−2” in FIG.9 represents signals written to pixels Pix included in pixel rowscoupled to at least two scanning lines 5 including a “second-to-lastscanning line 5” adjacent to the scanning line 5 positioned at the otherend of the display area 7 in the Y direction and a scanning line 5(third-to-last scanning line 5) adjacent to the “second-to-last scanningline 5” but not positioned at the one end in the writing period W of thefirst field period RF7. Specifically, “line 1” in “lower-order line 1”represents signals corresponding to pixels Pix on the first row. Inaddition, “line 2” in “lower-order 2 line 2” represents signalscorresponding to pixels Pix on the second row. In addition, “N−2” in“lower-order 2 LN−2” represents signals corresponding to pixels Pix onthe third row ((N−2)-th row) to the last row (N). In addition, “N−1” in“higher-order line N−1” represents signals corresponding to pixels Pixon the second row ((N−1)-th row) to the last row (N). In addition, “N”in “higher-order line N” and “lower-order line N” represents signalscorresponding to pixels Pix on the last row (N).

As described above, according to the fourth modification, a dispositionof a plurality of pixels Pix to which signals are written at a time inone of two writing periods W corresponding to the lower-order bits ofthe pixel signal is shifted in the first direction (Y direction) from adisposition of a plurality of pixels Pix to which signals are written ata time in the other writing period W. Thus, it is possible to restraininformation from being discarded between inputting and outputting andrestrain a shift in the first direction of pixels Pix to which signalscorresponding to the lower-order bits are reflected.

In FIG. 9, signals written to the scanning line 5 (for example, thescanning line 5 a) positioned at the one end of the display area 7 inthe Y direction and the scanning line 5 (for example, the scanning line5 b) positioned at the other end of the display area 7 in the Ydirection are controlled to be identical for the lower-order bitsubframe period LB3 and the lower-order bit subframe period LB7, butsignal writing to these pixel rows in the lower-order bit subframeperiod LB7 is not limited to this configuration but may be changed asappropriate. For example, the signal writing may be controlled such thatsignals written to the “second scanning line 5” are identical to signalswritten to the scanning line 5 a, and such that signals written to the“second-to-last scanning line 5” are identical to signals written to thescanning line 5 b. Alternatively the signal writing for the scanninglines 5 a and 5 b may be omitted.

The ratio between the light amount in each lighting period L of thelower-order bit subframe period LB3 and the light amount in eachlighting period L of the lower-order bit subframe period LB7 is, forexample, 1:1. However, the ratio is not limited thereto and may bechanged as appropriate.

Fifth Modification

FIG. 10 is a time chart illustrating exemplary field sequential controlin a fifth modification. Although FIGS. 3 to 9 exemplarily illustratecases in which the number of colors of light emitted from the lightsource 11 is three, FIG. 10 illustrates a case in which light in asingle color is emitted from the light source 11. In other words, thedisplay device 100 of the fifth modification is a monochrome displaydevice.

The frame period F1 in the fifth modification includes a higher-orderbit subframe period UB2, a lower-order bit subframe period LB8, and alower-order bit subframe period LB9. The higher-order bit subframeperiod UB2, the lower-order bit subframe period LB8, and the lower-orderbit subframe period LB9 each include one writing period W and onelighting period L. Signals written in the writing period W of thehigher-order bit subframe period UB2 are signals corresponding to thehigher-order bits of the pixel signal. Signals written in the writingperiod W of the lower-order bit subframe period LB8 are signalscorresponding to the lower-order bits of the pixel signal. In the fifthmodification, there is no color distinction because pixel signals aremonochrome. The idea of “signal corresponding to the higher-order bits”and “signal corresponding to the lower-order bits” in the fifthmodification is the same as the idea of “signal corresponding to thehigher-order bits” and “signal corresponding to the lower-order bits” inthe embodiment except that there is no color distinction.

Signals written in the writing period W of the lower-order bit subframeperiod LB9 are used for extended gradation expression that is set basedon the same idea as for signals in the lower-order bit subframe periodLB6 described in the third modification. However, the exampleillustrated in FIG. 10 is different from the example illustrated in FIG.8 in that such signal writing is performed in units of one pixel row (ona pixel row basis).

The present disclosure is also applicable to a configuration in whichlight in a single color is emitted from the light source 11 asexemplarily described in the fifth modification.

Sixth Modification

FIG. 11 is a time chart illustrating exemplary field sequential controlin a sixth modification. In the embodiment, in the frame period F1, thefirst field period RF2, the second field period GF2, the third fieldperiod BF2 of the lower-order bit subframe period LB2 are provided afterthe first field period RF1, the second field period GF1, and the thirdfield period BF1 of the higher-order bit subframe period UB1. However,in the sixth modification, the field periods included in thehigher-order bit subframe period UB1 and the field periods included inthe lower-order bit subframe period LB2 in the embodiment arealternately repeated. The sixth modification is the same as theembodiment except for this feature.

In the sixth modification, for example, as illustrated in FIG. 11, thefirst field period RF1, the second field period GF2, the third fieldperiod BF1, the first field period RF2, the second field period GF1, andthe third field period BF2 are provided, in the order as listed, in theframe period F1. In this manner, in the sixth modification, the order offield periods is controlled such that field periods of the same colorare discontinuous in time. When field periods for signals correspondingto the higher-order bits and field periods for signals corresponding tothe lower-order bits are alternately provided and the order of fieldperiods is controlled such that field periods of the same color arediscontinuous in time, it is possible to more reliably prevent visualrecognition of a pseudo contour and a color break by a user of thedisplay area 7.

The number of colors of light emitted from the light source 11 is notlimited to one or three but may be two, or four or more. In such a caseas well, in the same manner as the above-described embodiment andmodifications, control can be performed such that the light amount inone lighting period L, in which the light amount is larger than in otherlighting periods L, corresponds to the higher-order bits of a pixelsignal and the light amount in other lighting periods L corresponds tothe lower-order bits of a pixel signal. In addition, control can beperformed such that one frame period F1 includes a plurality of subframeperiods, each subframe period includes a writing period W and a lightingperiod L corresponding to one of a plurality of colors included in thelight source, continuous subframe periods correspond to differentcolors, one of the continuous subframe periods corresponds to thehigher-order bits of a pixel signal, and the other subframe periodcorresponds to the lower-order bits of a pixel signal.

It should be understood that, among other effects achieved by aspectsdescribed in the present embodiment, those clear from the presentspecification description or those that could be thought of by theskilled person in the art as appropriate are achieved by the presentdisclosure.

What is claimed is:
 1. A display device comprising: a display panelincluding a display area provided with a plurality of pixels; and alight source configured to emit light to the display panel, whereinwriting periods and lighting periods are alternately provided in oneframe period for at least one color, each writing period is a period inwhich part of a pixel signal is written to a corresponding one of thepixels, each lighting period is a period in which light is emitted tothe pixel after a corresponding one of the writing periods, and a lightamount in at least one of the lighting periods is larger than a lightamount in other lighting periods.
 2. The display device according toclaim 1, wherein the light source includes a first light sourceconfigured to emit light of a first color, a second light sourceconfigured to emit light of a second color, and a third light sourceconfigured to emit light of a third color, and the writing periods andthe lighting periods are provided for each of the first color, thesecond color, and the third color.
 3. The display device according toclaim 1, wherein the light amount in the one lighting period, in whichthe light amount is larger than in the other lighting periods,corresponds to higher-order bits of the pixel signal, and the lightamount in the other lighting periods corresponds to lower-order bits ofthe pixel signal.
 4. The display device according to claim 3, whereinthe display area includes a plurality of pixel rows arranged in a firstdirection, each of the pixel rows includes a plurality of pixelsarranged in a second direction orthogonal to the first direction, andthe lower-order bits of the pixel signals are written at a time to apredetermined number of pixels arranged in the first direction, thepredetermined number being equal to or larger than two.
 5. The displaydevice according to claim 4, wherein the lower-order bits of the pixelsignals for the predetermined number of pixels arranged in the firstdirection are averaged and written at a time to the predetermined numberof pixels arranged in the first direction.
 6. The display deviceaccording to claim 4, wherein two of the writing periods and two of thelighting periods corresponding to the lower-order bits of the pixelsignal are provided in one frame period.
 7. The display device accordingto claim 6, wherein a disposition of a plurality of pixels to whichsignals are written at a time in one of the two writing periodscorresponding to the lower-order bits of the pixel signal is shifted inthe first direction from a disposition of a plurality of pixels to whichsignals are written at a time in another writing period.
 8. The displaydevice according to claim 1, wherein the light amount in the onelighting period, in which the light amount is larger than that in theother lighting periods, corresponds to higher-order bits of the pixelsignal, the light amount in the other lighting periods corresponds tolower-order bits of the pixel signal, the one frame period includes aplurality of subframe periods, each of the subframe periods includes thewriting periods and the lighting periods corresponding to one of aplurality of colors included in the light source, continuous subframeperiods correspond to different colors, and one of the continuoussubframe periods corresponds to higher-order bits of the pixel signal,and another subframe period corresponds to lower-order bits of the pixelsignal.
 9. The display device according to claim 1, wherein the lightamount depends on a lighting time of the light source.
 10. The displaydevice according to claim 1, wherein the light amount depends onluminance of the light source.
 11. The display device according to claim1, wherein the display panel is a display panel in which apolymer-dispersed liquid crystal is enclosed between two facingsubstrates.
 12. The display device according to claim 1, wherein thelight source is provided on a side of the display panel.